To effectively manage our email, we have to accept a few basic truths. They’re hard truths, but that only makes them even more valuable. Here they are:
Matt Gammell has some great suggestions for taking care of your huge inbox queue. Truth be told, mine was pushing 20K.
This gave me the motivation to start tackling it.
Update: Several hours later and I'm still working on it; 17,343 messages still in the inbox. Also, somewhere between 873 and 1,378 messages iCloud will give you an error about deleting too many messages.